<section class="todoapp">
    <app-todo-header 
        placeholder="你想要干点啥"
        delay="100"
        (textChanges)="onTextChanges($event);"
        (onEnterUp)="addTodo();">
    </app-todo-header>
    <app-todo-list
        [todos] = "todos"
        (onRemoveTodo)="removeTodo($event);"
        (onToggleTodo)="toggleTodo($event);"
        (onToggleAll)="toggleAll();"
        >
    </app-todo-list>
    <app-todo-footer 
        [itemCount]="todos?.length"
        (onClear)="clearCompleted();">
    </app-todo-footer>
</section>